Musculoskeletal (MSK) disorders are a frequent reason for presentation to the emergency department (ED), encompassing a wide spectrum of conditions ranging from minor soft tissue injuries to limb-threatening infections or tendon ruptures. While radiography remains the initial imaging modality for many MSK issues, it lacks sensitivity and specificity for soft tissue abnormalities. In this context, high frequency US has emerged as an invaluable imaging tool, offering high-resolution evaluation of tendons, muscles, and subcutaneous tissues. The advantages of US in the ED setting are well established: it is non-invasive, radiation-free, and widely available. Despite these benefits, many emergency and general radiologists may feel less confident in performing and interpreting MSK US due to the specific skills it requires. This is particularly relevant in emergency contexts where tempestive diagnosis can significantly influence management and outcomes. This review aims to provide a practical and concise guide to the most relevant, high-yield applications of MSK US in the ED. It is primarily intended for general radiologists, while remaining relevant to other clinicians involved in acute musculoskeletal care, whether conducted within the radiology department or at the bedside. The applications of US covered in the article include the assessment of tendon ruptures, muscle injuries, bursitis, soft tissue infections, and hematomas, all of which are frequently seen in emergency settings. Emphasis is placed on typical clinical presentations, characteristic sonographic findings, and technical tips to improve diagnostic confidence.

Overview of common musculoskeletal ultrasound techniques

An effective MSK US examination relies on appropriate probe selection, scanning orientations, and dynamic maneuvers to optimize diagnostic accuracy and procedural safety. High-frequency linear transducers (typically 7–15 MHz or higher) are standard for superficial structures, while lower-frequency curvilinear transducers may be used for deeper tissues or in obese patients. Scanning orientations include longitudinal and transverse views, which are employed differently depending on the structure and pathology examined, often with comparison to the contralateral side to distinguish normal from abnormal findings. Dynamic examination is a hallmark of MSK US, allowing real-time assessment of joint movement and improving evaluation of various pathologies, particularly tendon integrity. Different dynamic techniques exist for major joints, often involving patient movement or stress maneuvers to reveal structures (e.g. supraspinatus tendon in the shoulder) or pathology not readily visible on static images. Additional techniques, such as graded compression and Doppler imaging, help differentiate soft tissue lesions and enhance vascular assessment (Table 1).

Table 1 Ultrasound assessment and management of most common tendon lesions and acute muscle tearsMuscle and tendon injuriesAchilles tendon rupture

Achilles tendon rupture is a common injury, especially in athletes, and requires accurate diagnosis for optimal recovery. US is highly sensitive for detecting acute ruptures, particularly when physical examination is limited by pain or swelling, demonstrating tendon discontinuity, retracted ends, hematoma, and loss of the normal fibrillar pattern [1,2,3]. Achilles tendon ruptures are typically categorized based on their anatomical location into three main types: (i) proximal ruptures at the musculotendinous junction, (ii) mid-substance tears involving the free tendon, and (iii) distal ruptures at the calcaneal insertion (enthesis). Among these, the most frequently reported site of rupture is the mid-tendon region, located approximately 4–6 cm proximal to its insertion on the calcaneus [4]. Sonographic assessment of the Achilles tendon is typically performed with the patient in the prone position, feet hanging over the edge of the examination table. This position facilitates both passive and active plantarflexion and dorsiflexion of the foot, which is essential for dynamic evaluation. Long-axis imaging is used to assess the tendon and surrounding structures during these movements, aiding in the detection of abnormalities in tendon continuity. The plantaris tendon, located medial to the Achilles, may be visualized in short axis as a small oval structure. US evaluation in the acute phase can be technically challenging due to pain, swelling, and hematoma formation, which may obscure the site of tendon discontinuity. In particular, hematoma or edema between torn tendon stumps may appear isoechoic and fill the defect, making it difficult to detect the rupture. A systematic long-axis scan extending from the distal enthesis at the calcaneus to the proximal musculotendinous junction of the soleus and gastrocnemius muscles is essential to localize the tear and assess its extent. Dynamic maneuvers can enhance diagnostic accuracy: during dorsiflexion from a plantarflexed position, the lack of synchronous motion between tendon stumps suggests a complete rupture (Fig. 1.) Observing tendon edge displacement with movement increases diagnostic confidence, especially when static imaging findings are equivocal [5].

Fig. 1

Complete rupture of the Achilles tendon at the mid-portion. A–a Sagittal US images show a normal fibrillar Achilles tendon at its mid-portion (A) and calcaneal insertion (a). B–b Long-axis images obtained during plantar flexion (B) and dorsal flexion (b) of the foot to magnify the separation of the torn ends of the Achilles tendon. A gap between the proximal (black arrowheads) and distal (white arrowheads) stumps is filled with anechoic fluid (asterisks), consistent with hematoma in the tendon bed

Distal biceps tendon rupture

Distal biceps tendon rupture typically affects middle-aged individuals, often during eccentric biceps contraction, and is strongly associated with male sex, smoking, and elevated BMI. Clinically, it presents with sudden pain, weakness in forearm supination, visible biceps deformity, and bruising [6]. US is an accurate tool for diagnosing distal biceps tendon ruptures, especially when combined with thorough clinical assessment and multiple scanning approaches. Four main US approaches are used—anterior, medial, lateral, and posterior—with operator preference influencing choice. The medial approach is often favored, but the anterior approach with the forearm pronated is also common. For less experienced operators, the medial approach is generally recommended. With the elbow flexed at 90° and the forearm supinated, the probe is placed longitudinally and medially over the distal arm. After identifying the brachial artery, the probe is shifted laterally to visualize the biceps tendon in its long axis. In case of tendon rupture, US typically reveals a loss of the normal fibrillar pattern, with a visible gap or discontinuity at the distal biceps tendon insertion site, often replaced by a hypoechoic area representing hematoma or fluid collection [7, 8]. The ruptured tendon may appear retracted proximally, sometimes with a visible mass or “balling up” of the muscle belly. Hypoechoic or anechoic regions adjacent to the rupture site indicate hematoma or fluid effusion (Fig. 2). Flexion and extension along with pronosupination maneuvre help differentiate between partial and complete tendon ruptures.

Fig. 2

Complete tear of biceps tendon. A-a Long-axis and short-axis US images show a normal distal biceps tendon (white arrows) inserting on the radial tuberosity (R). B-b Long-axis and short-axial US images demonstrate a complete tear of the distal biceps tendon (arrowhead). B The long –axis US image show hypoechoic fluid (asterisks) filling the distal bed of the retracted biceps tendon; the tendon itself is not clearly visualized. b Short-axis US image demonstrate the torn and retracted tendon at distal portion of the arm. R: radius

Quadriceps tendon rupture

Quadriceps tendon rupture is an uncommon injury, typically affecting men over 40 and often linked to conditions such as diabetes, gout, or chronic steroid use [9]. It usually presents with sudden knee pain, inability to extend the knee, and a palpable gap above the patella. While diagnosis is primarily clinical, imaging—particularly US and MRI—can accurately assess the extent of the injury. Partial tears may be treated conservatively, but complete ruptures require prompt surgical repair to restore function and prevent long-term disability. US represents a valuable initial modality for diagnosing quadriceps tendon rupture, especially when clinical assessment is inconclusive due to pain or swelling. US can accurately identify both complete and partial tears by visualizing disruption of the tendon fibers and associated hematoma, with high sensitivity but somewhat lower specificity compared to MRI, which remains the gold standard for definitive diagnosis and for resolving equivocal cases or suspected normal anatomical variants [10, 11]. US is particularly useful in the ED, allowing for immediate assessment and differentiation between partial and complete ruptures, which is crucial for timely surgical intervention and optimal outcomes [12].The superficial location of the quadriceps tendon makes it well-suited for sonographic evaluation, and dynamic imaging can further aid in assessing tendon function. The quadriceps tendon is a multilayered structure, with most studies identifying three or four distinct layers. The superficial layer is formed by the rectus femoris tendon, the middle layer(s) by the vastus medialis and vastus lateralis, and the deepest layer by the vastus intermedius tendon. Some studies have described a consistent three-layered arrangement, while others have found four layers, especially when accessory muscle heads are present, and even more complex variations in rare cases [13,14,15,16]. On US, a normal quadriceps tendon appears as a thick, linear, and echogenic structure inserting onto the patella. Partial ruptures may involve one or more of the tendon layers and typically present as focal hypoechoic defects within the tendon, sometimes with preserved continuity in the unaffected layers. In contrast, complete ruptures show disruption of all tendon layers, with the tendon ends separated by a hypoechoic or anechoic hematoma (Fig. 3). US can help distinguish between partial and complete tears by identifying which layers are involved and the extent of fiber disruption, though operator experience and patient factors (such as obesity) can affect accuracy. However, as previously mentioned, MRI is needed in some cases for precisely identifying the specific layer involved and guiding management decisions, as the number and thickness of injured layers influence treatment strategies and prognosis [17].

Fig. 3

Complete tear of the quadriceps tendon A-a Longitudinal US and sagittal MRI PD fat-sat images demonstrate normal appearance of the quadriceps tendon (arrows) at its insertion onto the patella. B-b Longitudinal US image and sagittal fat saturation PD MRI image demonstrate a complete tear of the quadriceps tendon, with proximal retraction of the tendon stump (arrowheads). A surrounding hypoechoic (US) and hyperintense (MRI) fluid collection (*) is visible

Patellar tendon rupture

Rupture of the patellar tendon is an uncommon yet severe injury, predominantly seen in physically active individuals under 40 [18, 19]. It usually results from a sudden, forceful extension of the knee against resistance—such as during jumping or sprinting—and often affects tendons compromised by chronic overuse, systemic conditions, or corticosteroid exposure [20]. Typical clinical findings include acute pain, knee swelling, an inability to actively extend the leg, and a high-riding patella (patella alta) evident on imaging, along with a palpable defect just below the patella. Patellar tendon ruptures most commonly occur as avulsion injuries at the inferior pole of the patella, accounting for over 80% of cases, while midsubstance and tibial avulsion tears are much less frequent [21]. The standard scanning approach of the patellar tendon involves both longitudinal and transverse scans, typically with the patient in a supine or standing position and the knee slightly flexed to optimize visualization of the tendon from the patella to the tibial tuberosity. Sonographic findings of patellar tendon rupture typically include a hypoechoic area within the tendon, indicating a tear, often accompanied by thickening of the tendon. In cases of partial rupture, US can quantify the lesion by measuring the length of the hypoechoic defect, which helps in grading the severity: Grade I (< 10 mm), Grade II (10–20 mm), and Grade III (>20 mm) lesions, with larger lesions correlating with a higher likelihood of requiring surgical intervention [22]. A cone-shaped, poorly echogenic area exceeding 0.5 cm in length in the center of the patellar tendon, along with localized thickening, is a reliable indicator of partial rupture or “jumper’s knee” [23]. In complete ruptures, US demonstrates a distinct gap in the tendon with retracted tendon ends, often accompanied by surrounding soft tissue swelling or hematoma in the tendon bed. In acute traumatic cases, sonography can also reveal avulsed bony fragments, and associated hematoma, all of which correlate well with surgical findings. Notably, studies consistently demonstrated excellent intra- and inter-rater reliability for US assessment of patellar and quadriceps tendon, even among operators with varying experience [24,25,26].

Rotator cuff tendon ruptures

Acute rotator cuff rupture is a sudden tear of the shoulder’s rotator cuff tendons, most often following trauma. Early surgical repair, ideally within 3 weeks, is associated with better functional outcomes, particularly in younger patients and traumatic tears. For small acute tears, both surgical repair and physiotherapy can achieve comparable short-term results, although nonoperative management carries a risk of tear progression over time [27,28,29]. The supraspinatus tendon is most frequently affected in acute rotator cuff tears, often presenting as a full-thickness rupture following trauma such as a fall [30]. Acute tears more commonly involve the subscapularis than degenerative lesions, with reported involvement in over 60% of full-thickness acute tears [31]. The infraspinatus and teres minor are less frequently involved in isolation but may be affected in larger or multi-tendon injuries [30, 31]. High-resolution US shows excellent diagnostic performance for full-thickness supraspinatus tears, with reported sensitivities ranging from 94% to 97% and specificities from 92.5% to 100%, closely matching the diagnostic accuracy of MRI [32, 33]. US evaluation of the subscapularis has a high specificity (often above 88%) but variable and generally lower sensitivity, especially for smaller or partial-thickness tears [taso34]. Optimal US examination of the rotator cuff tendons requires proper patient positioning: the supraspinatus is best assessed with the arm internally rotated and extended in the “modified Crass” position, whereas the subscapularis is evaluated with external rotation [35]. Both longitudinal and transverse scans should be obtained. Full-thickness tears appear as complete tendon discontinuity with fluid in the gap, whereas partial-thickness tears present as focal hypoechoic defects or fiber disruption (Fig. 4). In complete ruptures, tendon retraction and muscle trophism should be assessed to help distinguish acute from chronic tears. Therefore, report should specify tear presence, depth, location, and extent, noting insertional involvement or retraction, as well as associated muscle atrophy or fatty infiltration when visible.

Fig. 4

Full-thickness supraspinatus tear. Long-axis US image demonstrates a fluid-filled defect (asterisk) at the former insertion site of the supraspinatus tendon on the greater tuberosity (GT), with proximal tendon retraction (white arrows), consistent with a large full-thickness supraspinatus tear. GT: greater tuberosity

Finger flexor tendon ruptures

Finger flexor tendon ruptures most commonly involve the flexor digitorum profundus, flexor digitorum superficialis, and flexor pollicis longus tendons, and can result from various mechanisms such as crushing injuries, lacerations, hyperextension, or forced flexion against resistance [36]. The majority of ruptures occur at the tendon insertion or musculotendinous junction, but midsubstance ruptures have also been reported, sometimes without any predisposing disease or degeneration [36, 37]. Immediate re-repair is recommended for ruptured primary flexor tendon repairs in the fingers, particularly in zones 2 and 1 (respectively from the distal palmar crease to middle of the middle phalanx and distal to the middle of the middle phalanx), to maximize the chance of functional recovery and minimize complications from delayed intervention. Therefore, immediate imaging has a role for suspected finger tendon ruptures in the ED, especially when clinical assessment is inconclusive or injury severity is unclear. US has demonstrated high sensitivity and specificity for detecting complete tendon lacerations, and can also assess tendon gliding and retraction, which are important for surgical planning [38]. The US examination should be performed in both axial (transverse) and sagittal (longitudinal) planes: the probe is placed transversely and then longitudinally along the volar aspect of the finger; comparison with a normal finger can be helpful for non-expert operator [39]. Dynamic assessment is crucial: passive and active flexion and extension of the finger help visualize tendon movement and identify discontinuity, retraction, or lack of gliding, which are signs of rupture [40]. The distal tendon stump can be seen moving with passive joint motion, while the proximal stump is visualized during active flexion; gaps, loss of continuity, or abnormal tendon position confirm rupture.

Other tendon ruptures

Although rotator cuff and biceps tendon injuries represent the most frequently encountered tendon pathologies of the shoulder and upper arm, other tendon ruptures, though less common, must be recognized for their distinct clinical, anatomical, and imaging features [41]. Among these, pectoralis major and triceps brachii tendon ruptures are increasingly reported, particularly in active individuals engaged in high-demand physical activity such as weightlifting. Awareness of their typical mechanisms of injury, anatomical characteristics, sonographic appearances, and management options is important to ensure timely diagnosis and optimal functional outcomes.

Pectoralis major tendon rupture

Pectoralis major tendon rupture is an increasingly recognized injury that mainly affects young active men during eccentric muscle contractions, such as those in weightlifting. Common signs of pectoralis major tendon rupture include swelling, bruising, and deformity with loss of the anterior axillary fold. Patients often report weakness with pushing or arm adduction and may exhibit a dropped nipple or muscle bulge from retraction. Once swelling subsides, an indentation or asymmetry with medial retraction of the muscle belly becomes visible. The pectoralis major tendon inserts onto the lateral lip of the bicipital groove of the humerus, with a broad, flat footprint averaging about 73.3 mm in length and 3.3 mm in width [42]. The tendon results from the convergence of the two muscle heads: the clavicular and the sternal. The clavicular head is generally shorter and inserts more superiorly, whereas the sternal head is longer and inserts more inferiorly [43, 44]. Pectoralis major tendon ruptures most commonly occur at or between the myotendinous junction and the tendinous insertion on the humerus [45]. Optimal sonographic evaluation of the pectoralis major tendon is performed with the patient’s arm in slight abduction and external rotation. Scanning in both longitudinal and transverse planes allows for accurate identification of the distal tendon, which lies superficial to the long head of the biceps brachii tendon and inferior to the subscapularis. In the normal state, US demonstrates a fan-shaped convergence of muscle fibers twisting into a single tendon at its humeral insertion. The clavicular and sternal heads of the tendon can often be distinguished as separate echogenic components converging at the insertional footprint. Tendon tears results in disruptions of the normal fibrillar echotexture: as in the other tendon tears, partial-thickness tears typically appear as areas of reduced echogenicity with architectural disorganization, whereas full-thickness tears are characterized by complete fiber discontinuity, tendon retraction, and, in most cases, associated hematoma formation (Fig. 5). Operative repair is favored for most pectoralis major tendon and myotendinous junction injuries in active individuals, offering superior strength, function, and cosmesis compared to conservative management, though with some risk of complications. Nonoperative treatment may be considered for partial tears, muscle belly injuries, or low-demand patients, but often leads to persistent strength deficits and cosmetic concerns [46].

Fig. 5

Complete tear of pectoralis major tendon. A-a Axial US image and axial fat saturation PD MRI images demonstrate a full-thickness tear of the pectoralis major tendon (arrowhead) with complete retraction from the humeral insertion and associated fluid collection (*)

Triceps tendon rupture

Triceps tendon rupture is a rare injury (less than 1% of all tendon ruptures related to the upper extremity [47]), typically affecting middle-aged men, athletes, and weightlifters [48]. It usually results from a fall on an outstretched hand, forceful eccentric contraction, or direct elbow trauma [49]. As with other tendon ruptures, risk factors include anabolic steroid use, local corticosteroid injections, chronic renal failure, and metabolic bone disorders. Ruptures most commonly occur at the tendon’s insertion on the olecranon but can also involve the myotendinous junction [50]. Patients typically present with sudden posterior elbow pain, swelling, bruising, and weakness or inability to extend the elbow. A palpable gap above the olecranon and “boggy” swelling may be noted. The “flake sign” on lateral X-rays suggests bony avulsion. The triceps brachii tendon is formed by the convergence of its long, lateral, and medial heads, which have distinct origins. Anatomical studies have shown that the medial head has a separate, deeper insertion, while the long and lateral heads form a common superficial tendon [51]. All three components ultimately merge into a single unit at the bone. On US, the triceps tendon is best evaluated with the elbow flexed at 90°, both at rest and during dynamic maneuvers. Scanning is performed in longitudinal and transverse planes via a posterior approach, from the myotendinous junction to the olecranon insertion. The tendon is identified by its typical hyperechoic, fibrillar echotexture, and flexion-extension and medio-lateral movements aid in distinguishing the medial (deep) and lateral (superficial) tendon components. US reliably differentiates partial from complete tears and can detect selective involvement of individual heads, influencing clinical management [52]. Rupture is indicated by disruption of fibrillar architecture, tendon thickening, retraction, and hypoechoic or anechoic areas suggestive of hematoma. In avulsion injuries, bony fragments may be visualized (Fig. 6).

Fig. 6

Partial tear of the medial head of the triceps tendon. A-B Long axis and short axis US images demonstrate a partial tear at the myotendinous junction of the medial head of the triceps tendon. Medial tendon stump appears thickened and with heterogeneous echotexture (white arrowheads)

Acute muscle tear

Muscle tears are common sports injuries, often affecting muscles involved in eccentric contractions, such as the hamstrings and gastrocnemius [53]. They result from excessive stretching during muscle activation, typically causing tears at the myotendinous junction. Symptoms include acute pain and weakness, and diagnosis is usually based on clinical examination, with imaging reserved for unclear cases. On US, acute muscle tears may appear as hyperecogenic areas with distortion of normal architecture, indicating edema or hemorrhage, or as anechoic/hypoechoic areas of fibers disruption, which often represent more severe injuries with hematoma formation; compound lesions can show both features and suggest moderate to severe injury. Intrinsic muscle injuries, caused by simultaneous muscle contraction and elongation leading to myofiber damage, are classified into three grades based on US appearance [54, 55] (Table 2). Grade 1 injuries, characterized by minimal muscle tissue damage (< 5%), typically heal within 1–2 weeks. Grade 2 injuries involve partial lesions (>5%) without affecting the entire muscle. Grade 3 injuries, marked by complete rupture at the myotendinous junction associated with hematoma, require 5–8 weeks of recovery to reduce the risk of recurrence, the primary complication of these injuries [56].One of the most frequent muscle tear encountered in the ED is the strain or rupture of the medial head of the gastrocnemius muscle, often referred to as “tennis leg” [57, 58]. Sonographic findings in tennis leg typically reveal disruption of medial gastrocnemius aponeurosis or distal myoaponeurotic junction, with or without fluid collection between the medial gastrocnemius and soleus muscles, predominantly involving the myotendinous junction. The plantaris tendon, once thought to be a primary culprit of tennis leg, is now recognized as less frequently involved, with most cases attributable to the gastrocnemius [